According to the principle, a coaxial diplexer is based on a circular waveguide, which is known in the art. FIG. 1 is an extract from “Selected modes” by Spinningspark at Wikipedia™ and shows as a typical parameter of the circular waveguide the Transverse Electric (TE) mode 11, in short TE11 mode, wherein the dashed lines show the magnetic field in the cross section of the circular waveguide and the solid lines show the electric field in the cross section of the circular waveguide.
In principle, coaxial diplexers target an association of a first signal in a first, e.g., higher frequency band and a second signal in a second, e.g., lower frequency band in one common waveguide, wherein the first frequency band is different from the second frequency band. The reverse effect is also possible, i.e., a distribution of the first and second signal to two separate waveguides. Coaxial diplexers are accordingly to be assigned to the multiplexers, wherein in this case, two signals in two frequency bands are transmitted respectively via an inner and outer circular waveguide.
In this context the U.S. Pat. No. 3,922,621 B (the “Gruner” patent) discloses a coaxial diplexer, which uses corrugations in a cylinder-ring-shaped convexity, wherein the corrugations are designed as so-called TM11 resonators, in order to activate higher modes. The configuration of the corrugations as corresponding resonators for separating the first and second signal is realized by a corresponding geometry of the corrugations by reciprocal corrugation spacing and corrugation depth.